(a) Field of the Invention
The present invention relates to a discharging unit, a coater having the discharging unit, and an apparatus for coating the photosensitive material. More particularly, the present invention relates to a discharging unit for discharging a photosensitive material, a coater including the discharging unit, and an apparatus for coating a photosensitive material using the coater, so that foreign matters are efficiently removed from a target wafer and the photosensitive material is selectively coated on the target wafer.
(b) Description of the Related Art
A photosensitive material, which may be chemically reactive to light, is now widely used for a predetermined patterning of various kinds of thin films, such as oxide thin film, metal thin film, or semiconductor thin film, etc., so that the films perform a predetermined function thereof.
The photosensitive material, generally, requires a uniform thickness on the thin film to prevent processing failures. For example, when the photosensitive material is over-coated on the thin film, the photosensitive material on a portion of the thin film to be patterned is not completely removed, so that the thin film is insufficiently etched away during an etching process. In contrast, when the photosensitive material is not sufficiently coated on the thin film, the thin film is over-etched away since the thin film may be removed when the photosensitive material on a portion of the thin film to be patterned is partially removed. That is, when the photosensitive material is non-uniformly coated on a whole surface of the substrate, the thin film under the photosensitive material may be over-etched or under etched, finally causing process failures.
Generally, the photosensitive material is coated on the thin film by a spin coating process. When the photosensitive material is dropped on the substrate spinning with a high angular speed, the centrifugal force renders the dropped photosensitive material to spread in uniform thickness on the whole surface of the substrate, thus the photosensitive material is uniformly coated on the substrate.
However, even though the photosensitive material is not uniformly coated on a light and small substrate such as a wafer for manufacturing semiconductor devices, the spin coating process is disadvantageous to a heavy and broad substrate such as a liquid crystal panel. The broader and heavier the substrate is, the lower the angular speed is, and thus the photosensitive material is not uniformly coated on the substrate. In addition, when the angular speed of the liquid crystal panel is increased for improving coating uniformity, a corner portion of the substrate may be broken by the centrifugal force proportional to the angular speed sq. thereof, and the power for driving the substrate is inefficiently consumed.
A slit coating process is widely used for preventing the above-mentioned problems. According to the slit coating process, the photosensitive material is injected onto the substrate through the slit-shaped coater having a length much greater than a width thereof, and the photosensitive material is coated on the substrate by repeatedly moving the coater along a longitudinal or a latitudinal line of the substrate. The coater includes a body, an inlet potion, and an outlet potion. A containing space for containing the photosensitive material is formed in the body, and the inlet potion is formed at first side portion of the body. The outlet portion is formed into a slit shape, having a length much more than a width thereof, at a second side portion of the body facing the substrate.
However, the slit coating process has a problem that a marginal photosensitive material needs to be removed after completing the coating process in manufacturing an LCD device. The length of the outlet is similar to the width of a mother substrate, and the photosensitive material is coated on a whole surface of the mother substrate at a time. Meanwhile, the mother substrate is divided into a plurality of unit substrates, and in the end, the unit substrate is separated from the mother substrate. Each of the unit substrate is formed into the liquid crystal panel such as a thin film transistor (TFT) substrate and a color filter (C/F) substrate, respectively. A thin film for forming the TFT substrate or the C/F substrate is individually coated on each unit substrate. Therefore, the marginal photosensitive material, which is coated on a marginal region of the unit substrate on the mother substrate, needs to be removed, since the marginal photosensitive material is not necessary for forming the liquid crystal panel.
Therefore, the slit coating process is disadvantageous in that the processing time for the coating process is increased and the expensive photosensitive material is wasted. In addition, foreign matters floating in the air may easily stick to the mother substrate since the mother substrate does not rotate any longer, so that some voluminous foreign matters usually collide with the coater. That is, the foreign matters may easily cause damage a portion of the coater. Furthermore, the foreign matters move along the surface of the mother substrate together with the coater, thereby causing scratch on the surface of the mother substrate.